Facsimile systems are now well known, and this invention may be employed with any such system in which the final printing is defined by a bit map and in which the bit map may be modified before printing in accordance with this invention.
Modification of bit maps before printing is now well established, both for printers operating from highly accurate bit map data and for facsimile receivers. The modification is to eliminate the stairstep appearance of diagonal lines which results from printing which is applied to fill in certain bit locations and to leave the remaining bit locations entirely blank. Commercially, this modification is often described as enhancing the resolution of the printer. U.S. Pat. Nos. 4,437,122 to Walsh et al and 4,975,785 to Kantor are representative of such enhancement of resolution in printers. U.S. Pat. Nos. 5,060,082 to Matsumoto et al and 5,117,294 to Yano show such enhancement of resolution facsimile receivers.
This invention modifies the bit map of an image to correct errors. U.S. Pat. No. 4,646,355 to Petrick et al teaches modification of such a bit map to remove small dots and voids. U.S. Pat. No. 5,153,748 to Moyer is to the removal of gaps in such images. U.S. Pat. No. 5,151,794 to Kumagai teaches modification of such a bit map by determining a medium value for a group of pels.